Modal Stiffness and modal Mass in Ansys?

[urun4fun123]

For analysis outside ANSYS i need the Modal marix PHI and the modal stiffness defined by
[PHI]^T * [K] * [PHI]
the modal mass defined by
[PHI]^T * [M] * [PHI]

Using substructure and a modal analysis this is easyli done for a simple model by making an output file, and arranging the data in matlab. However if the system consists of severeal DOFS it would be far more complicated, since i have not figured out a generelized way to retrieve the data from the output files.

To specify my question:
Is it possible in ANSYS to get the diagonal matrices: the modal mass and the modal stiffness using PHI defined by a known number of modeshapes.

 

[meshparts]

If you have done a modal analysis, then you have the Eigenvalues and Eigenvectors. This is all you need. Using APDL you can easily write out the diagonal terms of the modal stiffness matrix: K_ii=(2*pi*f_i)**2

You don't have to care about the mass matrix, since the Eigenvectors are normalized to it -> modal mass matrix is the unity matrix.

The best way to write out the Eigenvectors (matrix PHI) is to fill an array with the data and then use the command *MWRITE. Another way is of course reading from Matlab the results file.

Hope this helps!

 

[urun4fun123]

Realizing that the modeshapes are normalized to mass by default was very helpfull. Thanks.

I addition to this:

If you for some reason need to normalize the mode shapes to unity, which I had too, there is a way to.
I found out that ANSYS calculates the kinetic energy by E_kin=1/2*[PHI]^T * [M] * [PHI]. Summing up the kinetic energi for each modeshape, the modal mass could be retrieved.